1. Field of the Invention
This invention relates to a development apparatus utilizing a magnetic one-component toner as developer.
2. Description of the Prior Art
There is known and has been broadly used such a development method utilizing a conductive, magnetic one-component toner as disclosed in U.S. Pat. No. 3,909,258 and others. In this development method, the toner is required essentially to be electrically conductive. The electrically conductive toner brought a certain difficulty in transferring the toner image on a latent-image carrying member onto a final-image supporting member such as conventional paper sheet or the like under an electric field.
In order to overcome such a problem in the prior art, the applicant had proposed improved development methods, for example, by U.S. patent application Ser. Nos. 58,434 and 58,435 (British Laid-open Patent Application Nos. 2,028,176 and 2,030,478). The proposed methods are characterized by the steps of applying a magnetic insulation toner onto a cylindrical developer supporting member having magnets contained therein, in a uniform thickness, and bringing the applied toner into a position opposed to a latent-image carrying member with no contact for development. At this time, a low-frequency alternating voltage is applied between the developer supporting member and the latent-image carrying member to cause the toner to reciprocate therebetween so that the development can be effectively made with excellent reproducibility in gradation, with no background fog and with no reduced ends of the image. In the methods, the transferring is facilitated since the toner is electrically insulative.
In the proposed development methods, it is extremely important to apply the toner onto the developer supporting member in a uniform thickness. If the toner layer has excessive thickness on the developer supporting member, the toner would not only contact with the latent-image carrying member, but also provide insufficient charge due to the friction between the toner and the developer supporting member. On the other hand, if the toner image has insufficient thickness, the developed image would be insufficient in density since the amount of the toner used in development is reduced.
There are methods for forming a uniform toner layer on the developer supporting member by use of an applying blade located at the outlet of a toner container as shown in FIGS. 1 and 2.
In such a method as shown in FIG. 1, a blade 1 of elastomeric material such as rubber or the like is contacted with a developer supporting member 2 under pressure to control the thickness of a toner layer 3.
In such a method as shown in FIG. 2, a blade 1a of magnetic material is located at a position opposed to one of the magnetic poles N.sub.1 of a fixed magnet 4 which is contacted with the inside of the developer supporting member 2. Toner particles 3 are stacked one above another along lines of magnetic force between the above magnetic pole N.sub.1 and the magnetic blade. The stacks of toner are swept by the edge of the blade to control the thickness toner layer under the action of magnetic force. See U.S. patent application Ser. No. 938,494, for example. (See British Laid-open No. 2,006,054).
In FIGS. 1 and 2, reference numeral 7 designates a developing device containing the toner 10, and reference numeral 9 denotes a latent-image carrying member such as a photosensitive drum in electrophotography and an insulator drum in electrostatic recording. The latent-image carrying member will be called a photoreceptor or photosensitive drum hereinafter.
In accordance with the above-mentioned methods, toner can be applied to the developer supporting member 2 to form the substantially uniform layer 3. In practice, however, it has been found in experiments that it may be difficult to stably form uniform toner layers on the above developer supporting member 2 over a prolonged period of time. It has been also found that it becomes more difficult to form uniform toner layers, particularly where the toner used is remarkably poor in flow characteristics, where the toner has aggregated, etc.
If the toner layer on the developer supporting member 2 (hereinafter called sleeve) has irregular thickness, the developed image also has irregularity so that a good image cannot be obtained. When such a phenomenon causing the irregularity was observed in detail, the following matters have been found:
When the toner layer is controlled in thickness by means of the blade 1a, the toner material protrudes outwardly at that portion of the blade 1a adjacent to the photoreceptor 9, shown by "A" in FIG. 2, to form a mass of toner 10.sub.1 in the portion A as shown in FIG. 3. When the mass of toner 10.sub.1 has grown to a critical amount, a portion of the toner mass is moved onto the sleeve 2 under the rotation thereof to form an irregularity in the toner layer as shown by 3' in FIG. 3. The irregularity 3' in the toner layer leads to any irregularity in the developed image. That is, the developed image will be irregular in density or have any fog corresponding to the irregularity in the toner layer. The irregularity 3' on the toner layer assumes varying shapes such as rectangular spots, corrugated spots, corrugated patterns and others which can be considered to produce depending upon the critical amount of the toner mass 10.sub.1 in the portion A, ambient factors and the like.
The applicant has proposed an effective method for overcoming problems involved by the above irregularity in the toner layer as disclosed in U.S. patent Ser. No. 138,909. This method prevents the toner irregularity from being produced on the toner layer by providing an irregular or rough surface on the above sleeve in the direction of movement. Such rough surface is considered to be effectively operative because the frictional force between the sleeve surface and the toner is increased to reduce the slipage therebetween so that the toner can protrude outwardly through the gap between the sleeve surface and the blade edge in a stable manner and because the toner mass of upstream the blade is periodically subjected to fine vibrations due to the circumferential irregularity of the sleeve surface so that the toner mass can be collapsed to bring the toner particles into good flow condition.